 First
constructed in 1930, the Lima Wastewater Treatment Plant consisted of
screening, grit removal, primary sedimentation, and anaerobic digestion.
Throughout the years, secondary treatment, tertiary treatment and
additional sludge digestion were added. In 1973, the plant was expanded
to an average dry weather flow capacity of 18.5 million gallons per day
(MGD) , and a peak flow capacity of 53.0 MGD. The design concept called
for secondary and advanced treatment portions of the plant to operate at
a peak rate of 33.0 MGD, with any remaining flow receiving primary
settling and chlorination. Since 1973 the plant has provided primary,
secondary and tertiary treatment, as well as biosolids recycling.
 Primary
treatment consists of screening, chemical treatment, grit removal and
primary settling. Plant influent is first treated by three self cleaning
bar screens which remove debris greater than 1/2 inch in diameter. After
screening, ferric/ferrous chloride is introduced into the flow stream to
help in phosphorous removal. Inert matter is removed in two 5000 gallon
grit removal tanks. After grit removal, polymers are added to the flow
to improve settling of organics. This settling is accomplished in seven
primary tanks with a combined volume of approximately two million
gallons.
Secondary treatment includes aeration and secondary settling. Primary
effluent and biologically activated sludge are mixed and flow through
one of five aeration basins. The aeration basins have a combined volume
of 5.5 million gallons. After being aerated for approximately eight
hours, the flow is routed into final settling tanks where the remaining
organic solids are removed. Total volume of final settling is 4.5
million gallons.
Tertiary treatment is provided by two nitrification towers,
disinfection through the use of chlorine, and de-chlorination.
Nitrification towers for ammonia removal were built in 1973 and were the
first municipal installation to utilize the packed tower process. These
towers have successfully met the plant's discharge permit conditions
without the need for final filtration or sedimentation. Chlorine is
applied to the tower effluent for disinfection. Sodium bisulfide is
added to the final effluent to remove any remaining chlorine prior to
discharging the treated water into the Ottawa River.
Anaerobic digestors treat the organics which have been removed
throughout the plant. The resulting biosolids product is either dried
through the use of vacuum filters or applied in liquid form to
surrounding agricultural ground.
Throughout the plant each stage of treatment is monitored and
controlled by a computerized process control system (PCS). Lima's
wastewater PCS consists of distributed programmable logic controllers
which are monitored using a desk top computer network. The PCS provides
monitoring, control, alarm notification and logging capabilities for
plant personnel.
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